German Published Patent Application No. 197 44 083 describes a system for detecting an imminent rollover of a vehicle. To that end, a critical rotational rate of the vehicle about its center of gravity is ascertained as a function of the measured angle of inclination of the vehicle. As can be gathered from this document, the critical rotational rate corresponds to a rotational energy of the vehicle which just exceeds the potential energy of the vehicle. Namely, if this is the case, that is to say, if the critical rotational rate is reached, then the vehicle will assuredly roll over. A prognosis should be made early as to whether the vehicle will roll over because of a specific driving maneuver, so that safety devices (e.g. airbags, rollover bars, etc.) existing in the vehicle can be triggered in time prior to the actual rollover. A rollover of a vehicle is very probable in the case of a driving maneuver in which, first of all, the center of gravity of the vehicle is raised by a specific height in the gravitational field of the earth, for example, when driving on a ramp, and secondly, the vehicle still has ground contact. During such driving on a ramp, the vehicle experiences a conversion of rotational energy into potential energy. So-called slope driving, during which the vehicle is traveling on a slope and thereby is on a slant, represents another driving maneuver which leads with high probability to a rollover of the vehicle. Different from driving on a ramp, in response to tilting due to a slope, potential energy is converted into rotational energy; namely, the vehicle tips down the slope without outer influences (apart from the gravitational force). A similar behavior as when driving on a ramp is exhibited by vehicles during extreme obstacle-avoidance maneuvers (e.g. fishhook, moose-avoidance test) or during lateral drifting with abrupt change of the friction coefficients (curb/soil tripped rollover). These two different types of driving maneuvers can lead to rollovers which give rise to a basically different movement of the passengers in the vehicle. To provide optimal protection to the passengers in all such cases, it is necessary to react to the different types of rollovers with correspondingly adapted triggering operations for restraint devices.
An object of the present invention is to specify a system for classifying various driving maneuvers that can lead to the rollover of a vehicle, which differentiates between various characteristic driving maneuvers so that a special triggering algorithm for restraint devices can be initiated for the driving-maneuver class determined in each case by the system.
The indicated objective is achieved in that an acceleration sensor is provided which measures the acceleration of the vehicle in the direction of its vertical axis, and that when the measured acceleration is above a threshold of 1 g, a classifier decides on a driving maneuver in which the vehicle lifts upward on one side as when driving on a ramp, and that in response to an acceleration between 0 g and 1 g, the classifier decides on a driving maneuver in which the vehicle tilts downward on one side as when driving on a slope.
According to the present invention, a differentiation is possible between two fundamental classes of driving maneuvers, namely as when driving on a ramp and when driving on a slope. These two driving-maneuver classes differ due to an opposite direction of their center-of-gravity acceleration. When driving on a ramp, the center-of-gravity acceleration is directed in the positive direction of the vertical axis of the vehicle, and when driving on a slope, is directed in the negative direction of the vertical axis of the vehicle. The passengers experience very different movements in response to both driving-maneuver classes which require different triggering of restraint devices in the vehicle.
It is expedient that the classifier does not implement a threshold-value decision based on the measured acceleration for deciding the driving-maneuver class until a rotational rate of the vehicle about its longitudinal axis, measured by a rotation-rate sensor, exceeds a predefined threshold.